In The Great Gatsby, how can readers tell Tom is a racist?
Tom informs Nick that he's a racist early on in the novel by mentioning the book he has just read, The Rise of the Colored Empires by "this man Goddard." He calls it a "fine book" and goes on to explain that the book argues that the white race is in danger of being "utterly submerged" by the darker races. He insists the book is "scientific" and that if whites, the "dominant race," don't watch out, the other races will seize "control of things."
Tom goes on to praise the "Nordics," in which he includes himself, Jordan, Nick, and after a tiny pause, Daisy, as the group that has produced "all the things that go to make civilization."
If that were not compelling proof that the man is an open and unrepentant racist, when he and Gatsby are having their confrontation in the Plaza Hotel over Gatsby having an affair with Daisy, Tom calls Gatsby "Mr. Nobody from Nowhere" and says that next society will "have intermarriage between black and white." Tom doesn't say this with approval, but with the intent to insult: someone like Daisy having an affair with someone like Gatsby (apparently not a "Nordic" in Tom's book) has started society down a slippery slope towards the racial mixing which Tom can't abide. Tom, at the top of society, wants to keep everyone else in their place.